As explained in document EP 2 607 884, when it is sought to protect the eyes of a wearer from ultraviolet radiation by means of spectacles, it is necessary to take into account not only radiation transmitted through the eyeglasses of these spectacles, but also rays reflected from the back face of these eyeglasses.
In this logic, the aforementioned document proposes to calculate an ESPF index that quantifies the overall reduction of ultraviolet radiation achieved by the spectacles in question and combines to do this a value of transmission through the spectacles and a value of reflection from the back face of the spectacles.
The ESPF index thus calculated makes an objective approach to evaluation of the protection from ultraviolet radiation provided by various spectacles possible.
In contrast, the protective needs of users are often poorly evaluated, in particular as regards the ultraviolet radiation reflected from the back face of eyeglasses. This is because this effect, which is not easily understandable by nonspecialists, is difficult to quantify, whereas a specific treatment of the back face of eyeglasses is necessary to prevent it.